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Cells
Cells for Tissue Engineering * The starting point for any attempt to engineer a tissue or organ substitute is a consideration of the cells that are to be employed * Considerations when selecting cells *# A supply of sufficient quantity, or rather, the off-the-shelf availability of the cells *#* For emergency surgeries *#* It is only with off-the-shelf availability that the tissue engineered products will be used for the wide variety of patients *# Free of pathogens and contamination *# Source (autologous, allogenic, or xenogenic) *# Type (stem cells or differentiated cells) Cell Source * Autologous ** Patient's own cells ** Immune acceptable ** Not viable for off-the-shelf applications * Allogenic ** Cells from another human source ** Viable for off-the-shelf applications ** May require engineering immune acceptance * Xenogenic ** From different species ** Not only requires immune acceptance, but must be concerned with animal virus transmission Differentiated Cells * Cells that are specialized for a particular function and do not maintain the ability to generation to generate other kinds of cells, or revert back to a less specialized cell * Present in adult tissues * There are more than 210 types of differentiated mammalian cells ** Blood Vessels: Smooth Muscle Cells, Endothelial Cells, Fibroblasts ** Heart: Cardiomyocytes ** Cartilage: Chondrocytes ** Bone: Osteoblasts ** Skin: Fibroblasts, Epithelial Cells * Many researchers are focused on using differentiated cells in engineered tissues ** Smooth muscle cells are used for engineering smooth muscle, blood vessels (with endothelial cells) ** Cardiomyocytes are used for engineering cardiac tissue like cardiac muscle ** Chondrocytes are used for engineering cartilage * Advantages of using differentiated cells ** in vitro proliferation in a controllable way ** Same cell type as in the target tissue can be used *** Cardiomyocytes to engineer cardiac tissue ** No ethical implications * Problems in using differentiated cells ** May have immune response if using allogenic cells ** Limited availability of autologous cells ** Limited proliferation capacity ** Each cell type has a different life span ** Can not culture cells from the elderly for very long Stem Cells * Stem cells are cells that have the ability to divide for indefinite periods in culture and give rise to specialized cells * Stem cells may solve many of the problems of using differentiated cells * Have the capacity to differentiate into different cell types ** BMSCs can differentiate into blood cells * Important in engineered tissues for tissues that don't have the ability to regenerate like cardiac tissue * Stem cells posses two properties ** Self-renewal, the ability to go through numerous cycles of cell division while maintaining the undifferentiated state ** Potency, the capacity to differentiate into specialized cell types *** Multipotent: can only differentiate into closely related family of cells. **** Ex. Hematopepoietic stem cells differentiate into blood cells *** Pluripotent: can differentiate into most tissues of an organism **** Ex. Embryonic stem cells Stem Cell Types * Embryonic Stem Cells ** Pluripotent stem cells that can differentiate into all of the specialized embryonic tissues * Adult Stem Cells ** Multipotent stem cells found in adult tissues